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FM Transmitter

FM Transmitter. FM Modulation using VCO. [1]. f out. V in. - Free Running Frequency of VCO. Corresponding DC bias. - Gain of VCO. Block Diagram. PA. . VCO. Input. DC Bias Vcc/2. Chipset. 4046 Phase-Locked Loop LM7171 Wide-Band Power Amplifier 741 Op Amp. 4046 PLL .

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FM Transmitter

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  1. FM Transmitter

  2. FM Modulation using VCO [1] fout Vin - Free Running Frequency of VCO Corresponding DC bias - Gain of VCO

  3. Block Diagram PA  VCO Input DC Bias Vcc/2

  4. Chipset • 4046 Phase-Locked Loop • LM7171 Wide-Band Power Amplifier • 741 Op Amp

  5. 4046 PLL Only use the VCO

  6. 4046 VCO Characteristic C1>=100pF

  7. Schematic

  8. PCB Layout Considerations • The signal traces should be short and wide to lower the impedance. • The width of the signal traces has to satisfy current driving capacity. • Any used board area should be shorted to ground to reduce AC noise. • Sockets and pads will induce extra capacitance, so components should be directly soldered to board. • Surface mount components are preferred over discrete ones for less lead inductance.

  9. PCB Layout

  10. Measured Results • Carrier Frequency: 15MHz • Bandwidth: Controllable • Output Power: 500mW

  11. FM Receiver

  12. FM Demodulation using PLL [2] PFD LF Ve in VCO

  13. Loop Filter Design [3]

  14. VCO Design • VCO free running frequency = Carrier Frequency • VCO Frequency Range is no smaller than Bandwidth • Large VCO gain will increase PLL natural frequency n and thus improves PLL tracking capability

  15. Block Diagram LNA Amp BPF PFD LF VCO

  16. Chipset • 4046 PLL • CLC425 Wide-band LNA

  17. 4046 PLL

  18. Schematic

  19. PCB Layout

  20. Superheterodyne FM Receiver

  21. Block Diagram IF Amp + IF Filter Input Matching Mixer Amp FM Demodulator LO

  22. Chipset • TDA7000 – FM Radio • LM3875 – Audio Power Amplifier

  23. TDA7000 [4]

  24. IF Filter

  25. Quadrature Demodulator Vout fin

  26. IF Harmonic Distortion IF=70kHz

  27. IF Distortion Suppression FLL

  28. Correlator To suppress interstation noise • Not Modulated • Lightly Modulated • Heavily Modulated

  29. Schematic

  30. PCB Layout

  31. Monolithic FSK Transmitter [5]

  32. PLL Reference Frequency Output Dual Modulus Prescaler Digital Input A/D Converter Shift Register Analog Input Clock Data Sampling Rate Block Diagram

  33. Inverter

  34. NAND – 2 Input

  35. NAND – 3 Input

  36. NAND – 4 Input

  37. NOR – 2 Input

  38. XOR

  39. Transmission Gate

  40. Edge-Triggered D Flip-Flop

  41. D Flip-Flop with ‘CLEAR’

  42. Voltage Comparator

  43. 8-to-3 Encoder

  44. A/D Converter

  45. Parallel-Serial Shift Register

  46. Phase-Frequency Detector

  47. VCO

  48. Dual Modulus Prescaler [6]

  49. Output Driver To drive capacitive load with minimum delay

  50. Capacitor Driving Capability CL=100p f=50MHz

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